A radiation imaging apparatus in which pixels, each combining a conversion element that converts radiation into charges and a switch element such as a thin film transistor (TFT) or the like, are arranged in a two-dimensional array has been widely used. In recent years, in consideration of increasing the multi-functionality of such a radiation imaging apparatus, incorporation of an automatic exposure control (AEC) function is being considered as one such function to be increased. The AEC function is used by a radiation imaging apparatus to obtain radiation irradiation information while radiation is being emitted from the radiation source.
Japanese Patent Laid-Open No. 2012-15913 discloses a radiation imaging apparatus in which a plurality of pixels including imaging pixels and radiation detecting pixels are provided in a matrix in a detection region for detecting radiation. The radiation detecting pixels are used to detect the start and end of radiation irradiation and to detect the cumulative radiation irradiation dose. Japanese Patent Laid-Open No. 2012-52896 discloses a radiation imaging apparatus in which imaging pixels and radiation detecting pixels are arranged and an image wiring line and a radiation detection wiring line to which signals generated in the pixels are output and a signal detection circuit for detecting signals from the image wiring line and the radiation detection wiring line are included. The image wiring line and the radiation detection wiring line have almost the same pattern, but radiation detecting pixels fewer than those on the radiation detection wiring line or no radiation detecting pixels are connected on the image wiring line. The signal detection circuit detects radiation based on a difference between the signal obtained from the image wiring line and the signal obtained from the radiation detection wiring line.